Electron discharge device



Oct. 4, 1960 A. w. SCHMIDT ELECTRON DISCHARGE DEVICE Filed March 3l, 1958 United States Patent O ELECTRON DISCHARGE DEVICE Adolph W. Schmidt, Norwood Park Township, Cook County, Ill., assigner to The Rauland Corporation, a corporation of Illinois Filed Mar. '31, 1958, Ser. No. 725,315

4 Claims. (Cl. 313-65) This invention relates to electron discharge devices such as X-ray image converters and more particularly to a novel method of increasing the output of a composite pick-up screen used in such image converters.

Most modern X-ray image converters consist of a substantially evacuated envelope containing a composite multiple layer pick-up screen, a uorescent viewing screen remote from the pick-up screen upon which a reproduction of an original source image is projected, and an electron optical system intermediate the multiple layer pickup screen and the uorescent viewing screen for the purpose of accelerating and focusing an electron image on the fluorescent viewing screen, to produce thereon a light I image of high intensity.

IIlhe composite multiple layer type pick-up screen usually consists of a phosphor layer, a barrier layer, and a photoemissive layer, all contiguous and applied to a relative thin radiation transparent light opaque supporting member. In operation, the phosphor layer is excited by impinging invisible radiation quanta which, in turn, generates an electron emission from the photoemissive snrface and that surface generally constitutes the cathode member of the electron optical system.

It is important to develop the most eicient phosphorphotoemissive multiple layer pick-up screen possible, and a phosphor such as silver activated zinc sulphide suspended in a resinous vehicle is frequently used in combination with a cesiated-antimony photo-electric surface. To achieve an etlicient multiple layer pick-up screen, it is vitally important that the eiciency'of the phosphorresin layer be as high Vas possible. Its eiiciency is dependent on several factors, including the following: the

Aamount of radiation quanta absorbed in such layerythe I energy eiciency of the phosphor itself; and the forward reflection of the light quanta emitted in the direction of the support member. It has also been found important that the adherence of the multiple layer pick-up screen to its support member be as substantial as possible.

It is therefore an object of this invention to provide an improved multiple layer pick-up screen for X-ray image converters characterized by a high diffuse rellective surface.

It is also an object of this invention to provide a multiple layer pick-up screen for X-ray image converters having improved adherence to its support member.

It is a further object of this invention to provide a multiple layer pick-up screen for X-ray image converters having an improved support member which is transparent Ato incident radiation and possesses a non-specular surface.

In accordance with the invention, a multiple layer pick-up screen for an image converter comprises a layer containing a phosphor responsive to incident radiation of one type to emit a corresponding radiation of another type. The phosphor layer is applied to a support member which is transparent to incident radiation and has an etched surface to which the phosphor layer is affixed.

'Ihe features of the present invention which are believed to be novel are set forth with particularity in the 2,955,218 Patented Oct. 4, v19v60 appended claims. 'Iheinvention together with further objects and advantages thereof may best be understood, however, by reference Ito the following description taken in connection with the following drawing in which:

Fig. l is a cross-sectional side view of an X-ray image converter according to the invention;

Fig. 2 is an enlarged view of a section of the multiple layer pick-up screen embodied in the image converter of Fig. l.

The image converter tube shown in the drawing comprises a substantially cylindrical glass envelope section 10 having an end portion in the form of a re-entrant press 11 and a substantially spherical glass envelope section 12 of a diameter approximately lequal to that of envelope section 10. Envelope sections 10 and 12 are presealed around their entire perimeters to respective metal flanges 13a land 13b which in turn are sealed together by heliarc welding or the like. Suitably mounted within the spherical shaped end section 12 is a substantially spherical composite pick-up `screen 14, the concave surface of which faces toward the re-entrant end of cylindrical envelope section 10. The re-entrant section 11 is closed by a llat glass plate 15 on the inside of which -a suitable iluorescent viewing screen 15a of silver activated zinc cadmium sulphide or the like is provided. To the inside of re-entrant section 11 is attached a metal anode 16 to which is attached a substantially spherical shaped cap 17 provided with an axial circular aperture 18 to provide access for electrons originating at multiple layer pick-up screen 14 to liuorescent viewing screen 15a. Anode 16 completely encloses and is electrically connected to fluorescent viewing screen 15a. The conveX'face of anode cap 17 faces the concave surface of composite pick-up screen 14. Sub stantially the entire cylindrical portion of envelope 10 is covered by electrode 19 in the form of a conductive Wall coating which may be of copper or the like and is electrically connected to metal liange 13a. The construction details of the image converter tube as thus far described may be entirely conventional and will be familiar to persons skilled in the art. f

In accordance with the invention the .multiple layer pick-up screen 14 comprises a sphericallylshaped sup-v port member 14a to which is applied a phosphorresin layer 14b. Contiguous to phosphor-resin layer.14b .is applied a barrier layer 14C over which is applied aphotoemissive layer 14d. Support member 14aY is composed of an X-radiation transparent kmaterialsuch as aluminum of a thickness .sufficient to rigidly support the multiple layers applied thereto. Phosphor-resin layer 14b consists of an X-ray sensitive phosphor such as silver activated zinc sulphide or the like embedded in a suitable organic silicon resin and applied to the spherical shaped aluminum supporting member 14a. Over this is applied a thin barrier layer 14C which may be of aluminum oxide or the like, of a thickness of approximately angstroms. Applied to the surface of Ibarrier layer 14e` is photoemissive cathode layer 14d which may be of the conventional cesiated antimony composition.

When an X-ray image is directed toward the convex surface of the multiple layer pick-up screen 14, the image passes through aluminum support member 14a and eX cites phosphor-resin layer 114b to produce a visible image of the impinging X-radiation. This visible or light image passes through barrier layer 14e and excites photoemissive layer 14d which generally constitutes the cathode member of the focusing and Iaccelerating lens system of t Vsui-sting of photoemissive cathode 14d, high voltage anode 16, and electrically conductive focus electrode 19, when energized with proper electrical potentials, causes the image to--be accelerated to and focusedrupon uorescen-t viewingscreen 15a. Y Y Y 4It has-'beenfo'und that etching the surfacel ofsuppoiting member 14a substantially increases therellectivity .of the supporting member, which higher reflectivity results Vin greater over-all efficiency lof the phosphor-resin light producing layer 14b. A sucient etch is accomplished .by immersingV the vsupporting member in a ten percent solution of sodium hydroxide for 15 to 20 minutes at a temperature -of approximately SOdegrees centigrade. In theY event vany problem is Aencountered in maintaining thickness control of the supportingmember, it can be etched on the concave face only, by depositing a ten percent solution Yof sodium hydroxide within the concave surface of-the'supporting member for approximately the same length of time and at the same approximate temperature. Neither the time nor the temperature is critical, except insofaras the material `thickness is aiected, which should -not be less lthan approximately V8 mils thickness to .maintainsuthcient rigidity. Various other methods exist yfor producing a non-specular surtace and the above method is merely illustrative, not restrictive.

As previously stated, it is extremely important that the eliciencyy of phosphor-resin layer 14b be as high as possible -and that `such ethciency is in part a function of the light quanta emitted in the direction of the support member'14a. It stands to reason, therefore, that the higher the diffuse reectivity produced in support member 14a the V`greater Vthe Vover-al1 ethciency of the phosphor-resin light producing layer 14b. Actual tests have indicated that' phosphor-resin layer 14h applied to a highly polished support member 14a produces substantially less light quanta that it does when applied to etched support member 14a. The exact reason for vthis is unknown, but it is believed it is due to the higher numericaly incident of possibility of reected light quanta from an etched'surface than that possible Vfrom the smooth surface. The improvement in brightness or light output is substantial from the phosphor-resin applied to the etched surface.

In additionto the previous gain, the adhesion of phosphonresin layer 1412 to etched aluminum support member I14a is substantially increased, contributing to a reduction in the number of reject units in producing such screens in production .thereby effecting substantial economies in 'l .quantity production.V t

While a particular embodiment ofthe present invention has been described, it is apparent that various changes and modiiications may be made, and it is therefore contemplated in the appended claims to cover all such changes and modifications as fall Within the true spirit and scope ofthe invention.

l. A multiple layer pick-up screen for an image converter comprising: a layer containing aphosphor responsive to incident radiation of one typelto emit `a correspondingV Vradiatio/n'of -another type; a support member for said layer which is transparentlo/'said incident radiation and has an etched surfaceto which said layer -is aixed and a photoenviissive` layer responsive to said other type radiation superimposed on said phosphor layer on the face thereof opposite said support member.

2. A multiple layer pick-up screen for an image converter comprising: a layer containing a phosphor suspended in a resinous vehicle'and responsive to incident radiation of one type to emit a corresponding radiation of another type; a support member for said layer which is transparent to said incident'radiation and has an etched surface to which said layer is aixed; and a photoemissive layer responsive to said other type radiation superimposed on said phosphor layer on the face thereof op,- posite Vsaid support member.

3. A multiple layer pick-up screen for an X-ray image converter comprising: a phosphor layer suspended in a resinous vehicle and responsive to X-ray radiation; a support member for said phosphor layer which is transparent to X-ray radiation and has a non-specular surface to which said X-ray sensitive phosphor layer is affixed; and a photoemissive layer responsive to radiation from said phosphor layer superimposed on Asaid phosphor layer on the face thereof opposite said support member.

'4. A multiple layer pick-up screen for an X-ray image converter comprising: a phosphor layer responsive to X-ray radiation; a support member for said `phosphor layer Which'is transparent to X-ray radiation and has an etched surface to which said X-ray sensitive phosphor layer is affixed; and a photoemissive layer responsive to .radiation from said phosphor Vlayer superimposed on said phosphor layer on the face thereof opposite said support member.

References Cited in the tile of this patent UNITED STATES `PATENTS 2,567,714V Kaplan n Sept. 11, 1951 '2,588,569 Picard c Mar. l1, 1952 2,680,205 Burton June 1, 1954 2,743,195 Longini Apr. 24, 1956 

